A method is known in which Mg, Be or Zn is doped so as to increase the resistivity of a Ga2O3 single crystal (see e.g., PTL 1). PTL 1 states that the resistivity of the Ga2O3 single crystal can be increased by adding 0.01 mol % or 0.05 mol % of Mg in growing the Ga2O3 single crystal by a FZ (Floating Zone) method.